Why is seawater salty?

Stone eroded on salt-bearing continents and followed the river to the sea. In fact, freshwater rivers carry a certain amount of dissolved minerals. Most of them are common table salt, sodium chloride. When salt reaches the sea it tends to stay there and accumulate.

Sodium chloride is very soluble in water and interconnected oceans in the world are very large, so this solution is not saturated and salt is not precipitated.

Earlier this century, it was thought that the age of the earth could be calculated by comparing the salinity of all the world's rivers with the salinity of the ocean. The number of theorists made about 300 million years. In fact, the earth's age is about 4.5 billion years.

The reason for the difference is relatively simple. The ocean's salty water enters the air, evaporates, dries, is blown into the continent and is reborn again into rivers, so their salt concentration is too high to be calculated. If we subtract the amount of salt that is roughly equal to the amount of salt being regenerated, we can get closer to the exact age of the earth. The concentration of salt in the sea changes slightly from place to place. For example, in the tropics, where there is heavy rain and near the mouth of a large river, the salt concentration is lower. The average concentration is about 3.5%, with 3/4 of that total in the form of sodium chloride salts.